A gas turbine engine may be used to power various types of vehicles and systems. A gas turbine engine may include, for example, four major sections: a compressor section, a combustor section, a turbine section, and an exhaust section. The compressor section raises the pressure of the air to a relatively high level. The compressed air from the compressor then enters the combustor section, where a ring of fuel nozzles injects a steady stream of fuel into a combustion chamber formed by two liners joined by a dome. The combustor dome may be made of a double wall to provide protection from hot gases. The double walled dome typically has an inner surface that may be referred to as a heat shield. After the injected fuel is ignited in the combustor, the energy of the compressed air significantly increases. The high-energy compressed air from the combustor section then flows into and through the turbine section, causing rotationally mounted turbine blades to rotate and generate energy. The air exiting the turbine section is exhausted from the engine via the exhaust section, and the energy remaining in the exhaust air aids the thrust generated by the air flowing through the bypass plenum.
Because combustors are subjected to high temperatures (e.g., temperatures in excess of 2000° C.), they may have limited service lives. In some cases, combustors may have high heat release rates. Thus, the liner, dome, or heat shield surfaces of the combustor may crack, oxidize, or become distorted. To improve the service life of the combustor the temperature of the liner, dome, or heat shield may be lowered.
Effusion cooling can be used to lower liner, dome, or heat shield temperatures. In this regard, a plurality of effusion holes, which are formed through the combustor liner, direct cooling air from outside of the combustor liner to an inner surface of the combustor liner (e.g., where the combustor liner is exposed to the high temperatures). As a result, the liner is cooled as air flows through each effusion hole and enters the combustor to form an air film to thereby isolate the high temperature gases from the liner. To enhance effusion cooling, the area and shape of effusion holes may be varied from a smaller circular inlet to a larger, diffusion shaped outlet. Varying the area of the effusion holes may cause the air to diffuse so that its velocity is reduced as the air film forms.
It is common practice to use computer targeted lasers to drill holes into metal surfaces, such as when forming effusion holes. Lasers are particularly useful in drilling holes into alloys of metal that are particularly tough to machine. Typically, effusion holes are formed in a combustor liner using percussion-on-the-fly laser machining, whereby a pulsating laser repeatedly strikes the liner until a row of holes are drilled therethrough. In order to improve manufacturing efficiency, the liner may be continuously rotated so that each laser pulse strikes a different hole during each complete rotation. A hole formed in this manner typically has approximately the same diameter as the laser beam. Thus, forming a shaped hole with an outlet having a shape that differs than that of the laser beam may significantly increase drilling time, as many additional laser strikes may be employed to form a single appropriately shaped outlet. Additionally, because a combustor liner may include thousands of these shaped holes, the manufacturing costs of drilling shaped holes using percussion techniques may be prohibitively high.
Hence, it is desirable to have an improved method for forming a plurality of shaped holes on a workpiece, such as a combustor liner to decrease manufacturing time.